In a sense, every material can be considered as a composite, even if the individual ingredients consist of atoms and molecules. The main objective in defining the permittivity ε and permeability μ for a medium is to present a microscopic view of the electromagnetic properties of the structure. Therefore, it is not surprising, if one replaces the atoms and molecules of the original composite with structures that are larger in scale, but still small compared to the wavelength to achieve an artificial meta-material with new electromagnetic functionality. The word “meta-materials” refers to materials beyond (the Greek word “meta”) the ones that could be found in nature.
Using the available materials in nature, one can easily obtain a dielectric medium with almost any desired permittivity; however, the atoms and molecules of natural materials or their mixtures prove to be a rather restrictive set when one tries to achieve a desired permeability at a desired frequency. This is particularly true in gigahertz range where the magnetic response of most materials vanishes. The ability to design materials with both ε and μ parameters would represent significant potential for advancing certain areas in wireless technology. In a paper, Pendry et al. showed that by embedding a metallic structure in the form of two concentric split rings (split-ring resonators), a medium with magnetic property could be achieved. However, the analysis presented is based on properties of an isolated split-ring resonator, that is, the effect of mutual interaction among the resonators once arranged in a periodic fashion is ignored. Thus the effective medium parameters so obtained are incorrect for the periodic medium. In addition, the geometry of split-ring resonator is not optimal for the design of artificial μ materials.